Just some points to bear in mind with an 0845 dial-up.
BT local call charges:-
Weekend (All Day Sat & Sun) - 1p/min
Mon to Fri - (After 6pm to before 8am) - 1.49p/min
Daytime - (Mon to Fri 8am to 6pm) - 3.95p/min
Minimum call charge 5p. All prices include VAT.
AFAIK, OneTel's 1p/min charge, including VAT, applies 24/7, with no minimum call charge. Uses an 0808 number.